1 /*
2 * include/asm-xtensa/rwsem.h
3 *
4 * This file is subject to the terms and conditions of the GNU General Public
5 * License. See the file "COPYING" in the main directory of this archive
6 * for more details.
7 *
8 * Largely copied from include/asm-ppc/rwsem.h
9 *
10 * Copyright (C) 2001 - 2005 Tensilica Inc.
11 */
12
13 #ifndef _XTENSA_RWSEM_H
14 #define _XTENSA_RWSEM_H
15
16 #ifndef _LINUX_RWSEM_H
17 #error "Please don't include <asm/rwsem.h> directly, use <linux/rwsem.h> instead."
18 #endif
19
20 #include <linux/list.h>
21 #include <linux/spinlock.h>
22 #include <asm/atomic.h>
23 #include <asm/system.h>
24
25 /*
26 * the semaphore definition
27 */
28 struct rw_semaphore {
29 signed long count;
30 #define RWSEM_UNLOCKED_VALUE 0x00000000
31 #define RWSEM_ACTIVE_BIAS 0x00000001
32 #define RWSEM_ACTIVE_MASK 0x0000ffff
33 #define RWSEM_WAITING_BIAS (-0x00010000)
34 #define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
35 #define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
36 spinlock_t wait_lock;
37 struct list_head wait_list;
38 };
39
40 #define __RWSEM_INITIALIZER(name) \
41 { RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, \
42 LIST_HEAD_INIT((name).wait_list) }
43
44 #define DECLARE_RWSEM(name) \
45 struct rw_semaphore name = __RWSEM_INITIALIZER(name)
46
47 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
48 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
49 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem);
50 extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
51
init_rwsem(struct rw_semaphore * sem)52 static inline void init_rwsem(struct rw_semaphore *sem)
53 {
54 sem->count = RWSEM_UNLOCKED_VALUE;
55 spin_lock_init(&sem->wait_lock);
56 INIT_LIST_HEAD(&sem->wait_list);
57 }
58
59 /*
60 * lock for reading
61 */
__down_read(struct rw_semaphore * sem)62 static inline void __down_read(struct rw_semaphore *sem)
63 {
64 if (atomic_add_return(1,(atomic_t *)(&sem->count)) > 0)
65 smp_wmb();
66 else
67 rwsem_down_read_failed(sem);
68 }
69
__down_read_trylock(struct rw_semaphore * sem)70 static inline int __down_read_trylock(struct rw_semaphore *sem)
71 {
72 int tmp;
73
74 while ((tmp = sem->count) >= 0) {
75 if (tmp == cmpxchg(&sem->count, tmp,
76 tmp + RWSEM_ACTIVE_READ_BIAS)) {
77 smp_wmb();
78 return 1;
79 }
80 }
81 return 0;
82 }
83
84 /*
85 * lock for writing
86 */
__down_write(struct rw_semaphore * sem)87 static inline void __down_write(struct rw_semaphore *sem)
88 {
89 int tmp;
90
91 tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS,
92 (atomic_t *)(&sem->count));
93 if (tmp == RWSEM_ACTIVE_WRITE_BIAS)
94 smp_wmb();
95 else
96 rwsem_down_write_failed(sem);
97 }
98
__down_write_trylock(struct rw_semaphore * sem)99 static inline int __down_write_trylock(struct rw_semaphore *sem)
100 {
101 int tmp;
102
103 tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
104 RWSEM_ACTIVE_WRITE_BIAS);
105 smp_wmb();
106 return tmp == RWSEM_UNLOCKED_VALUE;
107 }
108
109 /*
110 * unlock after reading
111 */
__up_read(struct rw_semaphore * sem)112 static inline void __up_read(struct rw_semaphore *sem)
113 {
114 int tmp;
115
116 smp_wmb();
117 tmp = atomic_sub_return(1,(atomic_t *)(&sem->count));
118 if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0)
119 rwsem_wake(sem);
120 }
121
122 /*
123 * unlock after writing
124 */
__up_write(struct rw_semaphore * sem)125 static inline void __up_write(struct rw_semaphore *sem)
126 {
127 smp_wmb();
128 if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS,
129 (atomic_t *)(&sem->count)) < 0)
130 rwsem_wake(sem);
131 }
132
133 /*
134 * implement atomic add functionality
135 */
rwsem_atomic_add(int delta,struct rw_semaphore * sem)136 static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
137 {
138 atomic_add(delta, (atomic_t *)(&sem->count));
139 }
140
141 /*
142 * downgrade write lock to read lock
143 */
__downgrade_write(struct rw_semaphore * sem)144 static inline void __downgrade_write(struct rw_semaphore *sem)
145 {
146 int tmp;
147
148 smp_wmb();
149 tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count));
150 if (tmp < 0)
151 rwsem_downgrade_wake(sem);
152 }
153
154 /*
155 * implement exchange and add functionality
156 */
rwsem_atomic_update(int delta,struct rw_semaphore * sem)157 static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
158 {
159 smp_mb();
160 return atomic_add_return(delta, (atomic_t *)(&sem->count));
161 }
162
rwsem_is_locked(struct rw_semaphore * sem)163 static inline int rwsem_is_locked(struct rw_semaphore *sem)
164 {
165 return (sem->count != 0);
166 }
167
168 #endif /* _XTENSA_RWSEM_H */
169